1. Field
The following description relates to ranging signal generation technology, and more particularly, to a method of generating a ranging signal of a wireless terminal and a device for generating a ranging signal of a wireless communication system that can generate the ranging is signal using one IFFT engine independently from a mode of the ranging signal transmitted in uplink in the wireless communication system in which a frequency interval of subcarriers used to generate an initial ranging signal and a frequency interval of subcarriers using periodic ranging are different.
2. Description of the Related Art
In general, communication systems have been mainly developed in voice services, and are being developed toward communication systems capable of supporting data services and a variety of multimedia services in addition to the voice services. Voice centered communication systems have a relatively small transmission bandwidth and require expensive usage fees so that it is difficult to meet increasing service needs from users.
Due to development of communication technology and increasing user needs for Internet services, communication systems capable of efficiently providing Internet services are increasingly required. Therefore, a broadband wireless communication system is introduced to provide efficient Internet services.
An orthogonal frequency division modulation access (OFDMA) method, which is a type of broadband wireless communication system method, converts a high speed data signal to a low speed data signal, and transmits and receives data through sub-channels including a plurality of subcarriers.
In the OFDMA method, downlink refers to simultaneously transmit signals to a plurality of users from a base station. Each user data signal is allocated to a plurality of sub-channels and the signal is transmitted as a downlink signal. In this case, all sub-subcarriers of signals transmitted from the base station have the same time delay and arrive in each user terminal at the is same time so that orthogonality between the sub-subcarriers is maintained and high speed data transmission is possible.
However, in uplink, due to independent propagation delay time and a relative location difference among user terminals, absolute time synchronization does not match between data signals arrived at the base station from user terminals so that the orthogonality is likely to be destroyed between the sub-subcarriers.
Accordingly, when the absolute time synchronization between uplink signals transmitted from user terminals does not match, signal orthogonality between subcarriers transmitted from a plurality of user terminals is destroyed and it is difficult to restore corresponding data in demodulation of signals received from the base station, thereby causing a serious data signal loss.
In order to address the above-described problems, the base station measures time errors based on a ranging signal transmitted from each user terminal through a uplink ranging procedure and informs the user terminal of the result. Therefore, the user terminal allows signals to be transmitted in accordance with reference time of the base station, thereby compensating propagation time errors between the user terminals.
In order to measure uplink time errors between the user terminal and the base station, each user terminal generates a random ranging code and transmits the code to the base station through a ranging channel. The signal received in the base station through the ranging channel shows a form of phase modulated signal having independent time delay.
The base station calculates correlation values between all random ranging codes provided from user terminals and ranging codes generated from the base station and finds a maximum value exceeding an arbitrary threshold value so that procedures for calculating time errors of each user terminal with respect to the reference time of the base station and finding a corresponding ranging code are performed.
Conventionally, since an initial ranging signal and a periodic ranging signal have the different number of OFDMA symbols used to transmit signals but have the same frequency interval of subcarriers, the same size of an inverse fast Fourier transform (IFFT) engine is used. Unlike conventional methods, a ranging signal generation method based on 802.16 m has a problem in that it is difficult to use with the same size of an FFT engine due to a difference between a frequency interval of subcarriers used to generate an initial ranging signal and a frequency interval of subcarriers using periodic ranging.
Technology disclosed in Korean Patent Application Publication No. 10-2012-0071920 (Jul. 3, 2012) processes signals of an initial ranging channel and a data channel using the same size of an FFT engine in a wireless communication system in which a frequency interval of subcarriers used to generate an initial ranging signal and a frequency interval of subcarriers using periodic ranging are different.
However, when a plurality of FFT engines having the same size are used, an appearance of a wireless terminal held by a user increases and power consumption increases due to complicated hardware.
Accordingly, the inventors studied technology that can generate a ranging signal using one IFFT engine independently from a mode of the ranging signal transmitted in uplink in a wireless communication system in which a frequency interval of subcarriers used to generate an initial ranging signal and a frequency interval of subcarriers using periodic ranging are different.